He chairs the Swiss Research Institute for Public Health and Addiction (Zürich) and is President of UNESCO Commission of Switzerland.
He specialized in human pathology and forensic medicine before becoming the head of Medical Services at the Bern University Hospital.
Under Zeltner's leadership, Switzerland developed in 1991 a pioneering illicit drug policy, which has received global attention.
The harm reduction policy of Switzerland – which includes large-scale syringe exchange programs (also in prisons)[3] and the medical prescription of heroin for chronic heroin addicts – was introduced against the strong opposition of the UN drug control authorities,[4] but endorsed by a majority of the Swiss population in several popular referendums.
All residents are required to buy insurance even if they are currently healthy, so that the risk pool remains reasonably favorable.
He was also Executive President of the WHO Regional Committee for Europe (1994–95) and Chairman of the Governing Council of the International Agency for Research on Cancer, (1998-2000).
[12] In this function he advised the Director General of WHO, Margaret Chan, in critical areas of the ongoing reform of this UN agency.
[13][14] The work was successfully completed by adoption of the Framework of Engagement with Non-State Actors (FENSA) by the World Health Assembly in May 2016.